Classic Dirt Bike — Autumn 2017

Above:Simply removethekick-start,gear

lever, allthecasescrews,footrestand

brakecross-overshaft,thenthecaseslips

offeasily...withabit ofwiggling.

Bigger balls

Theclutch,asusedona

Rotaxengineinamilitary

machine,is abit basic in

operation.It works... but

Wordsandpics:TimBritton cancertainly beimproved.

Thesimpleexplanationisit makesthe

bikeeasiertorideandyes,Iknowthat

goesforanymodificationorimprovement,

orevenjustservicing.Oftenthat’sall

somethingneeds,justtobelubricated

properly,butnotinthiscase,whatwas

neededherewasmodification.

Difficulty

Resources

Amillingmachine,someApriliaclutch

parts,anAllenkey,clutchcableandoil.

Suppliers

Sparessuppliers,lubricantsuppliers,

machineshop.

Why do it?

W

henlookingtomakeany

improvements,youwillneed

afewbits.Asstandard,the

militaryRotaxengineCan-Amhas

afairly simplemethodofactuatingtheclutch.

Insidethecasethereisarampcastandthis

hasthreepiddlinglittleballbearingsinit.A

pressedsteelfabricationridesuponthe

bearingsastheleverispulled.It workswell

enoughontheroadandevenonatrailride,

butinthecutandthrustofanenduro,things

getalittletougher.

Lastyear’sHotTr odVindurowasthefinal

strawformyclutchhand,asIrealisedby

theendoftheSundayallIwasmanagingto

dowastakeuptheslackinthecablerather

thanlifttheclutch.TheCan-Amgearboxisa

robustthingbutevensoit goesagainstthe

graintoabusemechanicalpartsinsucha

wayfortoolong.Somethinghadtobedone.

OneoftheadvantagesoftheRotax

engineisthenumberofcompanieswho

haveusedavariationofit tobuildtheir

ownmachines,ratherlikeVilliersengines

ofyearsago,sothereisawealthof

informationaround,plusafewspecialparts

hereandthere.

Askingaround,generalopinionwasthe

Apriliaversionoftheactuatorwasthe

wayforwardandoncethebitswereonthe

benchitwasobviousthiswasamoremeaty

methodofworkingtheclutch.

TheApriliakit requirestheoriginalramp

tobemachinedflatsothenewbaseplate

cansitsquarely.Suchworkisbeyondmy

workshopcapabilitiessoamachineshop

wassoughtandalargemillingmachine

madeshortworkoftherampandsoon

everythingfittedintoplace.Alittlelight

relievingonthecentralholetomakesure

nothingwasstickingandIlookedforward

toasimplerlifeformyclutchhand...until

it dawnedtheApriliaclutchcableentersthe

caseatadifferentpointtotheCan-Amand

theoperatingarmisslightlyoutoflinewith

theholeinthecase.

ActuallytheApriliausesadifferentcase

whichwouldhavebeenanoptionbutthis

wouldhavemeantconvertingtopre-mix

andIwantedtoretaintheauto-lubefacility

oftheoriginal.AlsotheApriliastyleclutch

caseisratherrarerthantheCan-Amone.

Luckily,mymachinistsaidit’snotaproblem

toaltertheactuatingarmandallwouldbe

well,butafterthatitwasmyjobtosortout

thefacespring.

Technical

feature

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